Hundreds of thousands of public-sector workers including teachers, council workers and firefighters have staged a 24-hour pay strike in a stoppage that has prompted David Cameron, the prime minister, to threaten a crackdown on union powers.
Protesters marched through the streets of many of Britain's main cities on Thursday in one of the biggest co-ordinated labour stoppages for three years.
It was earlier thought that up to a million people would stop work.
Denouncing what they called "poverty pay", they demanded an end to restrictions on wage rises that have been imposed by the government over the past four years in an effort to help reduce Britain's huge budget deficit.
In London, demonstrators marched towards Trafalgar Square at mid-day, chanting "Low pay, no way, no slave labour" to the beat of a drum.
A giant pair of inflatable scissors, carried by members of the National Union of Teachers (NUT), read "Education cuts never heal".
The biggest public-sector union involved, Unison, said early reports showed the strike had led to 3,225 school closures with more than 1,000 others partially closed.
Fall in real income
Refuse collectors, school support staff, cleaners, street sweepers, care workers, nursery assistants and social workers were joining the strike, Unison said.
Hot spots, it said, included the North East, Wales and East Midlands where most council offices had closed, while more than 60 picket lines closed most services in Newcastle.
"It is a massive decision by local government and school support workers to sacrifice a day's pay by going on strike, but today they are saying enough is enough," Dave Prentis, the general secretary of Unison, said in a statement.
Britain's coalition government has enforced a policy of pay restraint for public-sector workers since coming to power in 2010, imposing a pay freeze until 2012 and then a one percent pay rise cap, resulting in a fall in income in real terms.
The Cabinet Office played down the impact of the strike, saying that most schools in England and Wales were open and that fire services were operating throughout the country.
Cameron told parliament on Wednesday he planned to limit unions' powers to call strikes.
"How can it possibly be right for our children's education to be disrupted by trade unions acting in this way," he said.
Tough new laws would be proposed by the conservatives for next year's general election, Cameron said.
These would include the introduction of a minimum threshold in the number of union members who need to take part in a strike ballot for it to be legal.
The new legislation could also include the introduction of a time limit on how long a vote in favour of industrial action would remain valid.